THE SENATE'S rejection of the Comprehensive Test Ban Treaty last night was the product of short-term domestic political calculation. But it will resonate far beyond America's shores, and long after any political benefit here has worn off. It sets back incalculably an effort that stretches back decades to lessen the threat of nuclear war by barring any explosions of nuclear weapons.

There were serious arguments, arguments of substance, against the treaty, and serious people -- both inside and outside the Senate -- who opposed ratification. These people believe that a test ban would pose too great a risk to U.S. national security. They argued that, without testing, the reliability and credibility of the U.S. nuclear arsenal would erode over time, and that a treaty could not prevent America's adversaries from developing, perhaps clandestinely, nuclear arsenals of their own.

We believe that, on balance, the substantive arguments weighed far more heavily in favor of ratification. Experts with long experience in nuclear testing agree that computer simulation, if adequately funded, could ensure the reliability of the arsenal. Even were there some weaknesses in such simulation, no adversary could ever assume U.S. nuclear weapons would not work. The deterrent would remain sound. And while ratification could not guarantee that all other countries would follow the U.S. lead, it would clearly make such restraint more likely and more verifiable, at little or no cost to U.S. security. A test ban treaty would lock in a huge American advantage in nuclear technology.

The recklessness of last night's Senate action lies not only in the majority's unwillingness to ratify but also in some senators' determination to push ahead now for partisan advantage. Even Republicans who favored the treaty, or claimed to want a delay, lacked the courage to vote accordingly. Republicans understandably enjoyed the discomfort of Democrats who had pressed for an early vote, only to discover -- once their wish was granted -- that they could not prevail. It would have been understandable to let the White House and Democrats squirm for a time, to find a way to score a political point -- and then to do the right thing for the nation. That's not what happened last night.